In the post they mention that Götheborg had to adapt it's speed to the boat being towed, which probably limited the larger vessels sail-usage.

As another poster here, I also have a friend who has been able to sail on Götheborg once. The ship definitely have usable sails that are used most of the time. If I understand it correctly the motor is to some degree there as a modern safety requirement (and possibly it makes handling in port much easier, I would guess - don't know personally).